Military cargo aircraft are commonly loaded and unloaded through a cargo door and ramp located at the rear of the aircraft. The cargo door and ramp is typically raised and/or lowered to expose the interior of the aircraft in order to accommodate loading and unloading operations on the ground or to provide an opening through which cargo may be dropped from the aircraft during flight. Conventional cargo aircraft are configured such that the fuselage is substantially a cylindrical pressure vessel with the rectangular cargo door and ramp openings cut out of an aft section of the fuselage structure or empennage.
However, removing the fuselage section to create the cargo door and ramp openings weakens the fuselage. An aircraft fuselage is designed to bear many types of loads. First, the fuselage must support hoop stress created from the pressurization of the fuselage during flight. The fuselage must also support tension, compression, and shear forces caused by bending and torsion of the fuselage resulting from the movement of the aircraft flight surfaces used to control the aircraft, from the forces acting on the fuselage during landing, and from external air pressure and velocity changes such as those experienced while flying through turbulence or wind shear conditions.
The skin of an aircraft bears a large portion of these loads. The fuselage frame includes various stringers and bulkheads that further support the skin and the loads experienced during flight operations. When a portion of the fuselage is cut out, such as to accommodate a cargo door and ramp, the fuselage is no longer able to support the torsion, bending, and internal pressure inherent with aircraft flight. Moreover, cargo aircraft typically include long empennages to accommodate the large cargo ramps and doors required to load and unload the cargo bay. These long tail sections, coupled with the large structural cut-outs for the cargo doors and ramps present a rigidity problem.
The traditional solution to these issues includes incorporating a sill structure around the door and ramp cut-out. This reinforcing sill or frame structure stiffens the cut-out to support the required flight loads and rigidity requirements. However, the reinforcing structural members that are traditionally used to frame the cut-out undesirably increase the weight of the aircraft.
It is with respect to these considerations and others that the disclosure made herein is presented.